Photoelectric converter and fabrication method thereof

ABSTRACT

There is provided a laminated type photoelectric converter whose sensitivity is enhanced uniformly. In the photoelectric converter in which a photoelectric conversion device is laminated above a signal transfer device, the sensitivity is enhanced by providing bends on a lower electrode of the photoelectric conversion device and by confining light uniformly.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a photoelectric converter inwhich a photoelectric conversion device is laminated above a signaltransfer device and more particularly to improving the sensitivity ofsuch photoelectric converter.

[0003] 2. Description of Related Art

[0004] A photoelectric converter is an apparatus having photoelectricconversion devices. A photoelectric conversion device is a device forconverting light energy into electric energy or electric energy intolight energy. Among the photoelectric conversion devices, the device forconverting light energy (optical signal) into electric energy(electrical signal) includes a photovoltaic device (solar battery)aiming at generating energy and a photo-receiving device for processingsignals. The photo-receiving device includes a photo-diode and aphoto-transist or utilizing the photovoltaic effect and aphotoconductive cell utilizing the photo-conductive effect.

[0005] With the advancement of the technology of integrated circuits, animage sensor which is one of photoelectric converter and which is anapparatus in which photo-diodes or photo-conductive cells and signaltransfer devices are integrated on one and same device substrate hascome to be used widely.

[0006] Various measures are taken in the photoelectric conversion deviceused in the photoelectric converter in order to convert light energy(optical signal) into electric energy (electrical signal) efficiently.For instance, an electrode of the photoelectric conversion device isformed so as to have a texture structure to scatter light within thephotoelectric conversion device and to increase a quantity of energygenerated by the photoelectric conversion device (solar battery).However, because the scattering of light caused by the texture structureis probabilistic irregular reflection, it cannot be controlledintentionally and it is unable to increase electric energy (electricalsignal) uniformly.

[0007] What is drawing special attention lately among the photoelectricconverters is the image sensor. With the incoming of multi-media, adigital still camera, a cam-coder and the like using the image sensorare now rapidly spreading and the research on the improvement of theefficiency (conversion efficiency) for converting optical signalsentering the image sensor into electric signals is being activelyconducted. Because the photoelectric conversion devices and the signaltransfer devices are disposed on one and same plane of the same devicesubstrate in the image sensor, regions of the signal transfer devices ofthe image sensor turn out to be dead spaces where no photoelectricconversion can be made. Then, there has been proposed an image sensor inwhich a micro lens is provided in order to condense optical signals to aregion of the photoelectric conversion device in the photoelectricconverter.

[0008] There has been also proposed a laminated type image sensor asshown in FIG. 2 in which a photoelectric conversion device is laminatedon a signal transfer device to allot functions of photoelectricconversion and of signal transfer in the vertical direction. FIG. 2 is asection view of one pixel of the laminated type image sensor. In thelaminated type image sensor, the photoelectric conversion device 202 isformed on a substrate on which the signal transfer device 201 isintegrated. Because the dead space may be almost eliminated byconstructing the micro lenses as shown in FIG. 2, as compared to theimage sensor in which the photoelectric conversion device and the signaltransfer device are disposed on one and same plane, the area of thephotoelectric conversion device of the image sensor may be increased.

[0009] Although FIG. 2 shows a MOS image sensor using a top gate typeMOS transistor for the signal transfer device 201, the laminated typeimage sensor may be constructed by using a CCD image sensor in which aMOS capacitor is utilized for the signal transfer device and an imagesensor using another signal transfer device.

[0010] With the rapid spread of the image sensors, it is demanded tominiaturize and lower the cost of the image sensor further. In fact, thesize of the image sensors is becoming small year by year and the size ofan optical system which decides the size of the image sensor has reducedfrom {fraction (2/3)} inches in the 1980s to {fraction (1/4)} inches ofthe present day. Actually, an image sensor for a {fraction (1/4)} inchescamera is now being commercialized. The image sensor may be alsofabricated at low cost by miniaturizing the optical system of the imagesensor.

[0011] To obtain a high image quality image sensor having the same orhigher resolution with/over the prior art one while reducing its size,the image sensor must be densified by reducing the size of one pixel. Infact, the size of the pixel is becoming small along the reduction of thesize of the optical system of the image sensor and an image sensorhaving pixels whose size is 10 μm×10 μm or less is being commercialized.It is then expected that the reduction of the size of the pixel advancesfurther for the future.

[0012] When the size of one pixel of the image sensor is small, opticalsignals entering one pixel also decrease accordingly. Then, becauseelectric signals converted by the photoelectric conversion device of theimage sensor decrease, i.e., electric charges are generated less, therelative rate of noise generated by the electrical effects in and out ofthe apparatus to the quantity of generated electric charges increases,thus dropping the sensitivity.

[0013] As described above, there arises a problem that the sensitivityof the image sensor drops when the size of one pixel of the image sensoris reduced in order to obtain the small and high image quality imagesensor. The problem of the drop of the sensitivity of the image sensorwhich occurs when the size of the pixel is reduced cannot be solvedfully just by providing the prior art micro lens or by laminating thephotoelectric conversion device with the signal transfer device.

[0014] The sensitivity may be enhanced by increasing the quantity ofgenerated electric charges by confining light in a photoelectricconversion layer of the image sensor. However, when the photoelectricconversion device having the electrode in the texture structure is usedfor the image sensor, scattered light cannot be controlled and thesensitivity disperses among the respective pixels.

SUMMARY OF THE INVENTION

[0015] Accordingly, it is an object of the present invention to obtainan image sensor whose sensitivity is improved and having pixels havinguniform sensitivity.

[0016] It is another object of the present invention to obtain aphotoelectric converter, beside the image sensor, whose sensitivity isimproved and having photoelectric conversion devices having uniformsensitivity.

[0017] The sensitivity may be improved by converting optical signals(hereinafter referred to simply as light) which has entered thephotoelectric conversion device of the photoelectric converter intoelectric signals (hereinafter referred to as electrical charges)efficiently. In order to confine light uniformly, the present inventioncollects and controls light by utilizing reflection, condensation anddispersion of light, noticing on an electrode used in the photoelectricconversion device of the photoelectric converter.

[0018] A first arrangement of an inventive photoelectric converter ischaracterized in that in a laminated type photoelectric converter, anorganic resin film is provided above a signal transfer device, aphotoelectric conversion device is provided above the organic resin filmand a lower electrode of the photoelectric conversion device has bends.

[0019]FIG. 1 shows the first arrangement of the invention. FIG. 1 is asection view of one pixel of the photoelectric converter in which asignal transfer device 101 and a photoelectric conversion device 102 arelaminated. The photoelectric conversion device 102 comprises a lowerelectrode 104, a photoelectric conversion layer 106 and an upperelectrode 105. An organic resin film 103 is provided above the signaltransfer device 101 and the lower electrode 104 of the photoelectricconversion device has the bends.

[0020] As shown in FIG. 1 which shows the section of one pixel of thephotoelectric converter, the three bends are provided on the lowerelectrode of one pixel. That is, nine bends of 3×3 are created in onepixel of the photoelectric converter shown in FIG. 1.

[0021] The lower electrode 104 having the bends has a large lightconfining effect. It can also confine light uniformly because it has alight condensing function. Preferably, the disposition of the bends ofthe lower electrode is kept same in each pixel in order to prevent thesensitivity of each pixel from dispersing.

[0022] The sensitivity may be enhanced uniformly by providing bends alsoon the upper electrode to disperse light intentionally by the upperelectrode in reflecting the light condensed by the lower electrode 104again by the upper electrode 105 and by repeating the dispersion andcondensation by the upper and lower electrodes.

[0023] A second arrangement of the inventive photoelectric converter ischaracterized in that in the first arrangement of the invention, amaterial of the lower electrode of the photoelectric conversion deviceor of the surface thereof in particular is a metallic material selectedamong aluminum, molybdenum, tantalum, titanium, gold, silver andplatinum.

[0024] Because the first arrangement of the invention is characterizedin that the lower electrode of the photoelectric conversion device hasthe bends and light which has not been converted into electrical chargesis reflected and condensed by the bends, i.e., the reflected light iscondensed by the lower electrode, it is essential to use a materialhaving a high reflectance as the material for the surface of the lowerelectrode.

[0025] A third arrangement of the inventive photoelectric converter ischaracterized in that in the first or second arrangement of theinvention, the difference between the top and bottom of the bend of thelower electrode of the photoelectric conversion device is 0.25 to 4 μm.The difference between the top and bottom of the bend is limited by anultraviolet transmitting thickness of resist used in forming the bends.

[0026] The difference (110 in FIG. 1) between the top and bottom of thebend of the lower electrode of the photoelectric conversion device isinfluential in an angle of reflection. Because the present inventionreflects and condense light by utilizing bends, it requires bends havinga large difference between the top and bottom of a certain degree, i.e.,bends having a large angle of reflection of a certain degree.

[0027] The bend of the lower electrode of the photoelectric conversiondevice may be formed into the shape of a cylindrical lens, beside thatof a spherical lens.

[0028] A fourth arrangement of the inventive photoelectric converter ischaracterized in that in the first through third arrangements, the bendof the lower electrode of the photoelectric conversion device is largerthan a contact hole for connecting the lower electrode with the signaltransfer device and is smaller than one pixel.

[0029] The fourth arrangement of the invention will be explained byusing FIG. 1. As shown in FIG. 1, the size 111 of the bend of the lowerelectrode of the photoelectric conversion device is larger than thecontact hole 112 for connecting the lower electrode 104 with the signaltransfer device 101 and is smaller than the size 113 of one pixel.Although the photoelectric converter shown in the section view of FIG. 1has the three bends, it may have one or two bends or three or morebends.

[0030] A fifth arrangement of the inventive photoelectric converter ischaracterized in that in the first through fourth arrangements, amaterial of the organic resin film is an organic resin selected amongpolyimide, polyamide, polyimide-amide and acrylic resin.

[0031] It is noted that the signal transfer device in the presentspecification includes all of signal transfer devices having at least afunction for storing electrical signals converted by the photoelectricconversion device, a function for switching the functions for storingand reading signals and a function for selecting pixel position. It alsoincludes a signal transfer device having an amplifying function, besidethe reading function.

[0032] Therefore, although a MOS transistor is used in the signaltransfer device shown in FIG. 1, it is possible to use a MOS capacitor,a signal transfer device in which a MOS transistor and a MOS capacitorare combined or another signal transfer device. Then, although a MOStype image sensor is used as the image sensor in FIG. 1, it is possibleto use a CCD image sensor, a CID image sensor, a CPD image sensor and animage sensor in which they are combined.

[0033] Further, the use of the present invention allows a surface areaof the photoelectric conversion layer to be widened, thus enhancing theefficiency of the photoelectric conversion.

[0034] Although the photoelectric converter of the first arrangement ofthe invention may be fabricated, i.e., the bends may be created on thesurface of the lower electrode of the photoelectric conversion device,by etching the lower electrode isotropically, the bends are created onthe organic resin film below the lower electrode and then the lowerelectrode having the bends is created thereabove according to a sixtharrangement of the invention in order to create the uniform and smoothbends.

[0035] That is, the sixth arrangement of the invention pertains to amethod for fabricating the inventive photoelectric converter of thefirst arrangement, i.e., the photoelectric converter shown in FIG. 1.

[0036]FIGS. 1, 3 and 6 show the sixth arrangement of the invention, i.e.the method for fabricating the photoelectric conversion device shown inFIG. 1. At first, as shown in FIG. 3a, the signal transfer device 101 isformed on a substrate 107 and an organic resin flattening film 301 isformed above the signal transfer device 101. Next, a resist 302 isformed on the flattening film 301 as shown in FIG. 3b and bends arecreated on the resist 302 as shown in FIG. 3c. Then, the flattening film301 is etched almost in the same shape with the bends of the resist 303to obtain a structure shown in FIG. 3d. After that, the photoelectricconverter of the first arrangement is fabricated by creating a contacthole, by forming the lower electrode 104 of the photoelectric conversiondevice and by forming the photoelectric conversion layer 106 and theupper electrode 105 on the lower electrode 104 as shown in FIG. 1.

[0037] The bends shown in FIG. 3c are created on the organic resinflattening film 301 by using the method of forming the bends bypatterning the resist 302 and by etching it.

[0038] As the patterning method, there are methods of 1) adhering apattern on the substrate and exposing in batch and 2) using a stepperand a mirror projection aligner (MPA) to expose by focusing whilekeeping off the pattern from the substrate and 3) a proximity method.

[0039] With the miniaturization of the device, studies are conducted soas to increase the resolution as much as possible in general. Forinstance, an optical system is used in order to project the mask patternto the substrate with better resolution in using the method 2). Incontrary to that, the bends are created by lowering the resolution toblur the image and by making the patterning shape ambiguous in thepresent invention. Considering also that light may turn around becausethe substrate is separated from the mask, it is possible to create thebends.

[0040] Although it is a general practice to adjust the focusing depthand the position of the substrate by using an optical system in order toincrease the resolution, the focusing depth and the position of thesubstrate are shifted intentionally in the present invention. Thefocusing depth and the position of the substrate may be shifted byshifting the focusing depth by controlling the optical system or bymoving the position of the substrate.

[0041] The concrete method for creating the bends will be explainedbelow by using FIGS. 6 and 7. FIG. 6a shows a mask on which the patternin which circles are bored is printed. FIG. 6b shows a section view ofthe mask 601 along a line A-B in FIG. 6a and a section view of apositive type resist 602. The positive resist placed separately from themask is exposed by inputting light 605 from above the mask. The lightturns around because the resist is separated from the mask and part ofthe light advances obliquely. When the resist is exposed while shiftinga distance 603 between the mask and the resist a little from the focusedstate, a resist 604 having the concave bends whose patterning shape isambiguous as shown in FIG. 6c may be created.

[0042] Convex bends as shown in FIG. 7c may be created by using a mask701 in which circular patterns are printed as shown in FIG. 7a and whichis what the mask shown in FIG. 6a is reversed and by exposing a positiveresist 702 as shown in FIG. 7b in the same manner with the case of usingthe mask in FIG. 6.

[0043] Although the bends having the shape of the spherical lens hasbeen created in the cases shown in FIGS. 6 and 7, bends having a shapeof a cylindrical lens may be created by using a mask on which long andthin rectangular shapes are printed.

[0044] Either a positive resist or a negative resist may be used for theresist. The bends whose undulations are reversed may be formed byreversing the mask patterns as shown in FIGS. 6 and 7 when the same kindof resist is used. Further, when the same mask pattern is used, theconcave and convex bends may be both formed by appropriately using thepositive and negative resists. That is, the convex and concave bends maybe formed by selecting the mask patterns and the resists appropriately.

[0045] The bends may be created directly on the organic resin filmwithout using the resist by using a photosensitive polyimide for theorganic resin film (e.g., 301 in FIG. 3a) and by creating the bends bydirectly patterning the photosensitive polyimide as shown in FIG. 6. Asthe photosensitive polyimide, a negative resist having a product name ofPhotoneece and the like are available.

[0046] The difference 610 between the top and bottom of the bend of theresist shown in FIG. 6 is limited by a thickness 611 of the resist.Here, the thickness of the resist is a thickness through which theresist can be exposed, i.e., an ultraviolet transmitting thickness ofthe resist, and is 0.25 to 4 μm by the present technology. Accordingly,the difference between the top and bottom of the bend is within therange of 0.25 to 4 μm.

[0047] The size of the bend may be controlled by the mask pattern andthe shape of the bend may be changed by controlling the size and thedifference between the top and bottom of the bend. Preferably, the bendis formed into the shape having approximately a semi-spherical face of aspherical lens or a semi-columnar face of a cylindrical lens.

[0048] In the sixth arrangement of the invention, the resist 303 havingthe bends shown in FIG. 3c is formed by using the above-mentioned methodand is then etched to create the bends on the organic resin flatteningfilm 301 shown in FIG. 3. The etching is performed by using a method inwhich a selection ratio between the resist and the organic resin film isfrom 1 to 1 to 1 to 2 or preferably almost at 1 to 1.

[0049] The lower electrode, the photoelectric conversion layer and theupper electrode of the photoelectric conversion device are formed abovethe organic resin film having the bends thus fabricated. The bends ofthe lower electrode are created by using an inorganic material so thatthey are not flattened. It is also preferable to create thephotoelectric conversion layer and the upper electrode by usinginorganic materials because bends may be created also on the upperelectrode.

[0050] A seventh arrangement of the inventive photoelectric converter ischaracterized in that in the laminated type photoelectric converter, theorganic resin film 103 is provided above the signal transfer device 101,the photoelectric conversion device 102 is provided above the organicresin film 103, micro lenses 401 are provided above the upper electrode105 of the photoelectric conversion device and the lower electrode 104of the photoelectric conversion device has bends.

[0051] This arrangement of the photoelectric converter is what the microlenses are provided above the photoelectric converter of the firstarrangement of the invention.

[0052] Hitherto, one micro lens has been created in one pixel in orderto collect light to the photoelectric conversion device. However, it isnow possible to equalize the size of the photoelectric conversion devicealmost with the pixel by laminating the devices, so that it is notnecessary to collect light any longer.

[0053] Meanwhile, light may be taken into the photoelectric conversiondevice without loss by creating the micro lens on the surface of thedevice.

[0054] Although one each prior art micro lens aiming at condensing lighthas been provided per each pixel, there have been areas not covered bythe lens at four corners of the pixel because the pixel is square andthe micro lens is spherical. Then, the inventors et. al. have studiedalso on a number of micro lenses per pixel.

[0055] The areas not covered by the micro lens may be reduced byreducing the size of the micro lens and by disposing a plurality ofmicro lenses in one pixel so that there is almost no gap between them.Light ends up being absorbed by the micro lens itself if the micro lensis thick. However, the size of one micro lens is reduced and thethickness thereof may be thinned by providing the plurality of microlenses in one pixel, so that the loss of light may be reduced. Stillmore, a plurality of light condensing points are brought about bycreating the plurality of micro lenses, so that the conversionefficiency may be enhanced.

[0056] The size of the micro lenses may be the same with or differentfrom the size of the lower electrode of the photoelectric conversiondevice. Further, the position of the convex of the micro lens may bealigned with or deviated from the position of the concave or convex ofthe photoelectric conversion layer. However, it is preferable to alignthe position of the convex of the micro lens with the position of theconcave of the lower electrode because it turns out to be a doubleconvex micro lens whose efficiency is better than that of one-sideconvex micro lens.

[0057] Further, the disposition of the micro lenses in each pixel iskept same in order to equalize the sensitivity of each pixel as much aspossible. When there is a micro lens near the boundary of the cell, thesensitivity of the cell is influenced by a slight shift of thepatterning. Therefore, it is preferable not to dispose the micro lensnear the boundary of the cell.

[0058] An eighth arrangement of the invention pertains to a method forfabricating the photoelectric converter of the seventh arrangement. Thatis, it pertains to a method for fabricating the photoelectric converterin which the photoelectric conversion device 102 is laminated above thesignal transfer device 101, i.e., the micro lenses are created above thephotoelectric converter of the first arrangement, as shown in FIG. 4.The same method with the sixth arrangement is used up to the step offabricating the photoelectric converter of the first arrangement.

[0059]FIGS. 5 and 7 show the fabrication method thereafter. At first, anorganic resin flattening film 501 is formed above the upper electrode105 on the photoelectric conversion layer and a resist 502 is formedthereon as shown in FIG. 5a. When a positive resist is used for examplefor the resist, a resist 704 (i.e. 503 in FIG. 5b) having the convexbends as shown in FIG. 7c may be formed by patterning by using the mask701 as shown in FIG. 7. Then, the micro lenses shown in FIG. 4 may becreated by etching the resist such that the etching selection ratiobetween the resist and the organic resin film is from 1 to 1 to 1 to 2,or preferably almost at 1 to 1.

[0060] The specific nature of the invention, as well as other objects,uses and advantages thereof, will clearly appear from the followingdescription and from the accompanying drawings in which like numeralsrefer to like parts.

BRIEF DESCRIPTION OF DRAWINGS

[0061]FIG. 1 is a diagrammatic view of a laminated type image sensor;

[0062]FIG. 2 is a diagrammatic view of a prior art laminated type imagesensor;

[0063]FIGS. 3a through 3 d are diagrammatic views showing steps forfabricating the laminated type image sensor in FIG. 1;

[0064]FIG. 4 is a diagrammatic view of another laminated type imagesensor;

[0065]FIGS. 5a and 5 b are diagrammatic views showing steps forfabricating the laminated type image sensor in FIG. 4;

[0066]FIGS. 6a through 6 c show a pattern of a mask and section views ofthe mask and a resist; and

[0067]FIGS. 7a through 7 c show a pattern of a mask and section views ofthe mask and a resist.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0068] First Embodiment

[0069] A first embodiment pertains to a laminated type image sensor inwhich a lower electrode 104 of a photoelectric conversion device 102comprising the lower electrode 104, a photoelectric conversion layer 106and an upper electrode 105 has bends as shown in FIG. 1 and to afabrication method thereof.

[0070] Light may be collected and confined uniformly by creating thebends on the lower electrode 104.

[0071]FIG. 1 is a section view of one pixel of photoelectric converterof the present embodiment. In the photoelectric converter of the presentembodiment, there is provided a top gate type MOS transistor 101 havinga semiconductor layer having a source region 120, a channel region 121and a drain region 122 as well as a gate insulating film 123 and a gateelectrode 124. A polyimide film 103 is provided on the MOS transistor101.

[0072] A size 113 of one pixel is set at 10 μm×10 μm in the presentembodiment. However, the size of the pixel is not limited only to thissize.

[0073] Further, a material of the polyimide film 103 provided on the MOStransistor may be another organic resin such as acrylic resin, polyamideand polyimide-amide.

[0074] A PIN diode 102 is provided as the photoelectric conversiondevice on the polyimide film 103 in the present embodiment. An aluminumfilm 104 is provided as the lower electrode of the PIN diode 102 and anITO 105 is provided as the upper electrode. The aluminum film 104 hasthe bends.

[0075] Although aluminum having a large reflectivity among metals isprovided as the lower electrode of the PIN diode in the presentembodiment, a laminate of aluminum with titanium and molybdenum in whichaluminum is provided on the surface thereof may be used. Further,molybdenum, tantalum, titanium, gold, silver and platinum which aremetals having a large reflectivity beside aluminum may be used as thesurface material of the lower electrode.

[0076] Although the PIN diode is provided as the photoelectricconversion device in the present embodiment, another photodiode,photo-conductive cell or the like may be provided.

[0077] Further, preferably, the disposition of the bends of the aluminumfilm 104, i.e., the lower electrode of the PIN diode, is kept same pereach pixel in order to equalize the sensitivity.

[0078] The sensitivity may be enhanced more uniformly by providing bendsalso on the ITO to intentionally disperse light condensed by thealuminum film 104 when it is reflected by the ITO 105 and by repeatingthe dispersion and condensation of light by the upper and lowerelectrodes.

[0079] The fabrication steps of the photoelectric conversion device ofthe present embodiment will be explained with reference to FIGS. 1, 3and 6. At first, the top gate type MOS transistor 101 is formed and thepolyimide flattening film 301 of 5 to 10 μm in thickness is providedthereabove as shown in FIG. 3a.

[0080] Next, the positive type resist 302 is formed on the polyimideflattening film 301 as shown in FIG. 3b. The resist is formed so as tohave a thickness of 1 to 3.5 μm.

[0081] Then, the positive resist 302 is worked into a resist 303 havingthe concave bends as shown in FIG. 3c by slightly shifting a focusingdepth of an optical system from the focused state during the exposureand by using a mask 601 on which a pattern in which circles are bored asshown in FIG. 6a is printed. The mask 601 in FIG. 6a corresponds to onepixel and nine bends of 3×3 are formed in one pixel in the presentembodiment. A size 606 of the circles on the mask is designed to be 2 to3 μm.

[0082] A mirror projection aligner (MPA) is used for the exposure unit.The mask is patterned as the bends by slightly shifting the focusingdepth of the optical system of the MPA to blur the pattern in exposingthe resist. A difference between the top and bottom of the bend is 0.5to 3.5 μm which is almost same with or slightly smaller than thethickness 611 of the resist. A size 612 of the bend is 2 to 3.5 μm whichis same with or slightly larger than a diameter 613 of the circle of themask.

[0083] Next, RIE anisotropic etching is performed under the condition inwhich the etching rate is almost 1 to 1 in order to form the polyimidefilm 301 almost into the same shape with the bends of the resist 303shown in FIG. 3c. The RIE anisotropic etching is performed by usingetching gas in which CF₄/O₂ are mixed with a ratio of 5 to 95. Theetching selection ratio between the resist and the polyimide may be setat almost 1 to 1 by using this etching gas.

[0084] Although the RIE anisotropic etching is performed by using theetching gas in which CF₄/O₂ are mixed in the present embodiment, it isalso possible to perform the RIE anisotropic etching by using othermaterials and under other conditions by which the etching selectionratio between the resist and the polyimide becomes from 1 to 1 to 1 to2. It is also possible to etch the resist by the conventional dryetching. Thus, the polyimide film 103 having the concave bends as shownin FIG. 3d may be formed.

[0085] It is preferable to add a step of smoothing the surface of thepolyimide film by setting a pre-baking temperature of the polyimide filmand the resist at low and by baking the polyimide again after etchingthe polyimide almost in the same shape with the resist. At this time,the pre-baking is performed at 100 to 200° C. and the second baking isperformed at 250 to 350° C.

[0086] After creating the nine concave bends on the polyimide film ofone pixel, a contact hole is created and the aluminum film 104 is formedas shown in FIG. 1. The aluminum film 104 also has almost the sameconcave bends with the polyimide film 103. Thus, the concave bends whosereflectivity is large and which plays a role of condensing light areprovided on the lower electrode.

[0087] Then, the amorphous silicon 106 and the ITO 105 are formedfurther to fabricate the intended image sensor shown in FIG. 1. Theimage sensor fabricated as described above and having the structure asshown in FIG. 1 allows the sensitivity to be enhanced uniformly even ifthe pixel is miniaturized.

[0088] Although the MPA has been used as the exposing unit in thepresent embodiment, the image sensor may be fabricated by using astepper which allows a focusing depth to be controlled. The proximitymethod may be also used.

[0089] Further, although the difference between the top and bottom ofthe bend has been 0.5 to 3.5 μm in the present embodiment, it may be0.25 to 4 μm. Still more, although the size 111 of the bend shown inFIG. 1 has been 2 to 3.5 μm in the present embodiment, it will do if itis larger than the contact hole for connecting the lower electrode withthe signal transfer device and is smaller than the pixel.

[0090] Second Embodiment

[0091] A second embodiment pertains to a photoelectric converter inwhich a plurality of micro lenses are created above the image sensor ofthe first embodiment and to a fabrication method thereof.

[0092] The conversion efficiency may be enhanced by providing theplurality of micro lenses above the photoelectric conversion device ofone pixel.

[0093]FIG. 4 is a section view of one pixel of the image sensor of thepresent embodiment. Three micro lenses 401 made of acrylic resin areprovided above the photoelectric conversion device 102 of the imagesensor of the first embodiment in the section view of FIG. 4. That is,nine micro lenses of 3×3 are provided on one pixel.

[0094]FIGS. 5 and 7 show steps for fabricating the image sensor of thepresent embodiment. At first, a flattening film 501 made of acrylicresin and having a thickness of 5 to 10 μm is formed on the ITO 105which is the upper electrode of the photoelectric conversion layer ofthe image sensor of the first embodiment and a positive type resist 502having a thickness of 2 to 4 μm is formed thereon as shown in FIG. 5a.

[0095] Then, a resist 704 (which corresponds to a resist 503 in FIG. 5b)having the bends as shown in FIG. 7c is formed by using a mask 701 (maskon which circle patterns are printed) on which a mask pattern that isalmost inverse to the mask used in the first embodiment is formed and bypatterning in the same manner with the first embodiment. The mask 701corresponds to one pixel and the pattern of 3×3 circles is printedthereon. Accordingly, nine micro lenses may be formed on one pixel. Asize 710 of the circle of the mask in FIG. 7a is 2 to 4 μm and thecircles are disposed in the same manner with the mask in the firstembodiment. Although the mask 701 shown in FIG. 7a is used in thepresent embodiment, the pattern of the mask may be different.

[0096] Then, the micro lenses 401 shown in FIG. 4 may be created byetching the resist 503 such that the etching selection ratio between theresist 503 and the acrylic resin flattening film 501 becomes from 1 to 1to 1 to 2 or preferably almost 1 to 1.

[0097] The resist film is etched by using etching gas in which CF₄/O₂are mixed in a ratio of 5 to 95 to create the acrylic resin film havingconvex curved faces. Although the etching gas of CF₄/O₂ is used in thepresent embodiment, another etching method in which the etchingselection ratio between the resist 503 and the organic resin film 501 is1 to 1 may be used.

[0098] The convex bends may be created by using the same positive resistby thus changing the mask pattern from that of the first embodiment.

[0099] The conversion efficiency may be enhanced by providing theplurality of lenses in one pixel like the present embodiment. Further,the double convex micro lenses 401 whose conversion efficiency may beenhanced more than the one-side convex micro lenses may be created bycreating them so that the mask pattern of the lower electrode of thephotoelectric conversion device corresponds to the mask pattern of themicro lenses.

[0100] As described above, the present invention can enhance theconversion efficiency by utilizing the reflection, condensation anddispersion of light and can enhance the sensitivity which has beenproblematic in reducing the size of the pixel of the image sensor.Further, because the present invention allows light to be controlled byintentionally condensing it, the sensitivity per pixel, which has beenproblematic in the prior art image sensor, may be equalized.

[0101] The present invention can enhance the sensitivity of not only theimage sensor but also of the photoelectric converter having thephotoelectric conversion devices and can equalize the sensitivity.

[0102] Further, the use of the present invention allows the limit of thesize of one pixel in terms of the sensitivity to be reduced further.

[0103] While the preferred embodiments have been described, variationsthereto will occur to those skilled in the art within the-scope of thepresent inventive concepts which are delineated by the following claims.

What is claimed is:
 1. A laminated type photoelectric converter in whicha photoelectric conversion device is laminated above a signal transferdevice, wherein an organic resin film is provided above said signaltransfer device, said photoelectric conversion device is provided abovesaid organic resin film and a lower electrode of said photoelectricconversion device has bends.
 2. A converter according to claim 1,wherein a difference between a top and bottom of said bend is 0.25 to 4μm.
 3. A converter according to claim 1, wherein said bend is largerthan a contact hole for connecting said lower electrode with said signaltransfer device and is smaller than a pixel.
 4. A converter according toclaim 1, wherein a material of a surface of said lower electrode of saidphotoelectric conversion device is a metallic material selected amongaluminum, molybdenum, tantalum, titanium, gold, silver and platinum. 5.A converter according to claim 1, wherein a material of said organicresin film is organic resin selected among polyimide, polyamide,polyimide-amide and acrylic resin.
 6. A laminated type photoelectricconverter in which a photoelectric conversion device is laminated abovea signal transfer device, wherein an organic resin film is providedabove said signal transfer device, said photoelectric conversion deviceis provided above said organic resin film, micro lenses are providedabove an upper electrode of said photoelectric conversion device and alower electrode of said photoelectric conversion device has a bend.
 7. Aconverter according to claim 6, wherein a difference between a top andbottom of said bend is 0.25 to 4 μm.
 8. A converter according to claim6, wherein said bend is larger than a contact hole for connecting saidlower electrode with said signal transfer device and is smaller than apixel.
 9. A converter according to claim 6, wherein a material of asurface of said lower electrode of said photoelectric conversion deviceis a metallic material selected among aluminum, molybdenum, tantalum,titanium, gold, silver and platinum.
 10. A converter according to claim6, wherein a material of said organic resin film is organic resinselected among polyimide, polyamide, polyimide-amide and acrylic resin.11. A method for fabricating a photoelectric converter in which aphotoelectric conversion device is laminated above a signal transferdevice, comprising steps of: forming said signal transfer device on asubstrate; forming a flattening film made of organic resin above saidsignal transfer device; forming a resist on said flattening film;creating a bend on said resist; etching said flattening film almost inthe same shape with said bend; forming a lower electrode of saidphotoelectric conversion device; and forming a photoelectric conversionlayer and an upper electrode above said lower electrode.
 12. A converteraccording to claim 11, wherein a difference between A top and bottom ofsaid bend is 0.25 to 4 μm.
 13. A converter according to claim 11,wherein said bend is larger than a contact hole for connecting saidlower electrode with said signal transfer device and is smaller than apixel.
 14. A converter according to claim 11, wherein a material of asurface of said lower electrode of said photoelectric conversion deviceis a metallic material selected among aluminum, molybdenum, tantalum,titanium, gold, silver and platinum.
 15. A converter according to claim11, wherein a material of said organic resin film is organic resinselected among polyimide, polyamide, polyimide-amide and acrylic resin.16. A method for fabricating a photoelectric converter in which aphotoelectric conversion device is laminated above a signal transferdevice, comprising steps of: forming said signal transfer device on asubstrate; forming a flattening film made of organic resin above saidsignal transfer device; forming a resist on said flattening film;creating a bend on said resist; etching said flattening film almost inthe same shape with said bend; forming a lower electrode of saidphotoelectric conversion device; forming a photoelectric conversionlayer and an upper electrode above said lower electrode; and formingmicro lenses above said upper electrode.
 17. A converter according toclaim 16, wherein a difference between A top and bottom of said bend is0.25 to 4 μm.
 18. A converter according to claim 16, wherein said bendis larger than a contact hole for connecting said lower electrode withsaid signal transfer device and is smaller than a pixel.
 19. A converteraccording to claim 16, wherein a material of a surface of said lowerelectrode of said photoelectric conversion device is a metallic materialselected among aluminum, molybdenum, tantalum, titanium, gold, silverand platinum.
 20. Ac converter according to claim 16, wherein a materialof said organic resin film is organic resin selected among polyimide,polyamide, polyimide-amide and acrylic resin.